Prader-Willi syndrome (PWS) is a unique genetic disorder caused by the loss of paternally expressed genes in the q11-q13 region of chromosome 15. Although much progress has been made in recent years in the understanding of the genetics of PWS, little is known about the behavioral-affective aspects of PWS, particularly in the area of social functioning. Anecdotally, parents report that their children with PWS have great difficulty establishing and maintaining friendships with their peers, and that their behavior is often inappropriate, particularly in response to emotional situations (Alexander & Greenswag, 1995). Although social skills deficits (Holm 1981) and limits in establishing affective relationships (Peri et al, 1984) have been superficially addressed in the literature, there has been no systematic study of the social functioning of children with PWS. Recent work suggests a potential source of social difficulty for children with PWS, namely, their ability to understand and respond to the emotional behavior of others (Sullivan & Tager-Flusburg, 1998). The purpose of the proposed research is to begin to investigate these two components of affective functioning in young children with PWS. To address this aim, we have developed a series of experiments designed to tap: 1) the perceptual and cognitive aspects involved in understanding other's emotional behaviors, and 2) children's affective responses to other's emotional behaviors. The investigators predict that young children with PWS will perform equivalently to a group of match controls on tasks assessing the perceptual and cognitive aspects of understanding the emotional behavior of others. They also predict that despite being able to understand the emotional behavior of others, young children with PWS will provide significantly fewer appropriate behaviors in response to others behaviors than a matched control group. This pattern of performance would suggest a deficit in the affective rather than cognitive aspects of social functioning in young children with PWS.